1. Field of the Invention
This invention relates to a pickup or transducer for musical instruments. In particular, the invention relates to a pickup for a guitar comprising one or more piezo-electric crystals mounted within a framework for detecting sound from the guitar and transmitting it via a cable to an amplifier.
2. The Prior Art
It is often desired to amplify the sounds made by an acoustic guitar, without altering the quality of sound made by the guitar. A common way to do this is to attach a transducer, or pickup, to the guitar. The pickup detects the sounds of the guitar and transmits the sounds to an amplifier via a cable. The pickup is typically made with piezoelectric crystals, such as that described in U.S. Pat. No. 3,624,264 to Lazarus, the disclosure of which is herein incorporated by reference.
The drawback to this standard pickup is that the pickup must be mounted in a very precise manner on the guitar. Any deviation from a perfect mounting position will cause the vibrations detected by the crystals to cancel each other out and the sound will be distorted. The precise mounting position is determined by the guitar's “sweet-spot” and typically resides on the right side of the guitar under the bridge (or on the left side for left-handed guitars). This spot is very small and difficult to detect in a precise manner. In addition, variations in the position of the piezo crystals during manufacturing further increases the difficulties in locating the optimum position for the pickup, resulting in very poor repeatability from guitar to guitar, and from pickup to pickup. This constitutes the major disadvantage that has prevented its application on a high volume or OEM basis. Consequently, many pickups are mounted incorrectly and do not transmit the sound properly.
U.S. Pat. No. 6,448,488 to Elhaus refers to a very complicated method of achieving a similar output signal using three crystals mounted at different points around the bridge of the guitar, each crystal being representative of a different axis. These are combined and then electronically processed to obtain a potentially dephased signal. U.S. Pat. No. 5,206,449 to McClish uses two transducers to provide a dephased signal.
Transducers that employ large sensing areas, continuous sensors or multiple sensors that are not isolated are especially susceptible to severe time, phase and frequency errors. These transducers are ubiquitous in the marketplace. However, they carry intrinsic fundamental phase and time delay problems that “smear” the sound of the pickup and cannot be overcome or compensated for with additional electronics or in combination with additional sensors or sensor types.
The common major defects of the current transducers are as follows:                1. Difficulty in setup: the transducer requires a “unique” location to compensate for various phase, time and amplitude errors. The transducer location is not repeatable and requires constant adjustment to get a good tone. The difficulty in setup also prevents such a transducer from being installed by the instrument manufacturer to achieve a uniform sound quality, unit to unit. A fundamental characteristic of this transducer defect is that a small change in location, i.e., 0.005″, would lead to drastic changes to the tonal qualities.        
2. Unstable tonal response: different playing styles yield widely different tonal qualities. This is the result of the interaction between the time and frequency components in the signal. One fundamental characteristic of this defect is that a particular combination of instrument and a particular transducer may sound acceptable for one playing style, i.e., finger style, but would sound completely unacceptable for another style, i.e., strumming. The common solutions being offered on the market are “blender” systems combining multiple transducers or microphones as an attempt to compensate for the unstable tonal response of the primary pickup. Although quite popular, these systems rarely achieve completely acceptable tonal qualities for all situations.
3. Insufficient frequency flatness and bandwidth: this is most evident given the increase in usage of more frequency equalization. Some models offer graphic equalizers on the side of guitars in an attempt to compensate for poor frequency response of the transducer. One fundamental characteristic of such a system defect is the very poor sound quality when the controls are set flat.